The present invention pertains generally to matrix wire printers and more particularly to movable wire print position shift apparatus utilized in matrix printers to provide high quality, high-speed printing characteristics.
A clear advantage of matrix printers over prior art printers, such as daisy wheel printers, is the ability of matrix printers, to provide high-speed printing in a device which is both economical and reliable in operation. Matrix printers utilize a series of print wires that are formed in a linear array having a closely spaced configuration in the vertical direction. Because the matrix print wires are circular in shape, the imprintation of the print wire forms a sequence of dots which approximates solid lines. Adjoining arcuate sections of the sequence of dots, however, produce void sections which degrade the quality of the print. In other words, a solid consistent imprintation to form a high quality solid line is not produced because of the voids generated by the adjoining arcuate sections.
These problems have been reduced by the prior art by providing a larger number of print wires to increase the imprintation area and form a more consistent solid line during imprintation. However, voids still exist between the joining arcuate sections so that the quality of the print continues to be somewhat degraded.
To overcome these disadvantages and limitations of the prior art, print heads with wire shifting apparatus were developed, such as disclosed in U.S. Pat. No. 4,010,835, issued Mar. 8, 1977, to Martin, et al, which are capable of reprinting a line of print with the printing wires shifted by a predetermined amount. Consequently, during the reprinting process imprintation is made in the voids between the dots to provide a more consistent imprintation which, consequently provides a much higher quality print.
Various other types of shifting mechanisms for wire matrix print head devices are shown in U.S. Pat. Nos. 3,759,359 of Stellmach, 3,882,985 of Liles, 4,400,101 of Hendrischk, and 4,459,051 of Kawai, the disclosures of which are incorporated herein by reference thereto. In general, these prior patents disclose the use of actuating mechanisms mounted externally of the wire housing for causing pivotal displacement of the entire wire housing or pivotal displacement of a wire bearing and guide member attached to a spring-type armature member mounted outside the wire housing. At the present time, there have been some attempts to mount pivotally supported wire shift apparatus within the confines of the wire housing by use of spring-type cantilevered armature support devices which are flexibly displaceable by associated electromagnetic apparatus.
Disadvantages of such prior art devices are that they are generally complex, expensive, lack efficiency, bulky and are not easily assembled or adjusted.